JP5191464B2 - Lithographic pattern dividing method, lithography processing method and device manufacturing method including the dividing method, and mask manufactured by the dividing method - Google Patents

Description

[0001] The present invention relates generally to a lithographic apparatus, and more particularly to an exposure method using multiple exposures.

A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning device, alternatively referred to as a mask or reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (eg including part of, one, or several dies) on a substrate (eg a silicon wafer). The pattern is usually transferred by imaging onto a layer of radiation sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. A conventional lithographic apparatus synchronously irradiates each target portion by exposing the entire pattern to the target portion at one time and a so-called stepper and a substrate parallel or antiparallel to a predetermined direction ("scan" direction). And a so-called scanner that irradiates each target portion by scanning the pattern with a radiation beam in a predetermined direction (“scan” direction) while scanning.

[0003] As used herein, the term "projection system" refers to, for example, refractive optics systems, reflective optics, as appropriate to other factors such as the exposure radiation used or the use of immersion liquid or vacuum. It should be construed broadly to cover any type of projection system, including systems, catadioptric optical systems, magneto-optical systems, electromagnetic optical systems and electrostatic optical systems, or any combination thereof. Any use of the term “lens” herein may be considered as synonymous with the more general term “projection system”. The radiation system may also include components that operate according to any of these design types to direct, shape, or control the radiation projection beam. Radiation and projection systems generally comprise components for directing, shaping or controlling the radiation projection beam. In general, the projection system comprises means for setting the numerical aperture of the projection system (commonly referred to as “NA”). For example, an adjustable NA stop can be placed inside the pupil of the projection system. The radiation system typically comprises adjustment means for setting the outer and / or inner radius range (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution upstream of the mask (inside the pupil of the radiation system). .

[0004] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more patterning device tables). In such “multi-stage” machines, additional tables can be used in parallel, or one or more other tables can be used for exposure while one or more tables perform the preliminary process can do. The lithographic apparatus may be of a type in which the substrate is immersed in a liquid having a relatively high refractive index, such as water, so as to fill a space between the final element of the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. As used herein, the term “immersion” does not mean that a structure, such as a substrate, must be submerged in liquid, but rather that liquid exists between the projection system and the substrate during exposure. .

[0005] Circuit patterns corresponding to individual layers of an IC device typically include a plurality of device patterns and interconnect lines. The device pattern can include various spatially arranged features such as, for example, a line-space pattern (“bar pattern”), a capacitor contact pattern, a contact hole pattern, and a DRAM isolation pattern. A feature is not necessarily characterized by a shape in which line elements define a closed contour. For example, the spatial arrangement of the tips of two adjacent features and the space between the two tips can be referred to as features for purposes of this specification and the claims.

[0006] For the purposes of this specification and the claims, the size of a feature refers to the nominal size that the feature has at the substrate level. At the mask location, the feature size is M times the nominal size, where M is the magnification of the projection system (usually | M | = 1/4 or 1/5). In general, further size shifts in the mask are introduced to compensate for errors that occur, for example, between pattern projection and exposure. Such sub-pattern feature resizing is hereinafter referred to as biasing and / or optical proximity correction (OPC). The amount of biasing and / or OPC is also generally expressed as a nominal amount corresponding to a size change at the board level. The term “target” when used in expressions such as “target features” indicates that these features have approximately the nominal size desired for the device layer.

[0007] Fabrication of circuit patterns includes control of space tolerances between features, between interconnect lines, and between feature elements, and control of feature and feature element sizes. As the demand for the number of features per printed die area has increased, resolution enhancement techniques have been developed to increase the resolution limits that can be achieved with lithographic processing methods using projection lithographic apparatus. . The minimum space between the two lines allowed in the fabrication of the device layer and / or the minimum width of the line or any other feature, such as a contact hole, is called the critical dimension (CD). Features that include a minimum size approximately equal to the CD are referred to herein as “CD-sized features”.

[0008] Optimum performance of a lithographic processing method and the use of a lithographic projection apparatus with the ultimate resolution lithographic processing of a pattern comprising an array of CD sized features (eg contact holes, etc.) separated by a distance approximately equal to CD Is generally necessary. In an array of such features, a periodic pitch P can be defined in this example that is approximately equal to twice the CD. The pitch of P = 2CD is the smallest pitch that CD size features can be configured for printing with lithographic processing methods. This layer may also include CD-sized features located in one or more arrays with a pitch greater than 2CD. In particular, printing of layers containing CD sized contact holes arranged at both minimum and larger pitches is important and can include state-of-the-art super-resolution means. In general, features separated by a line to space ratio of 1: 1 to 1: 4 are considered “dense features”, but features separated by a distance greater than about 10 times the imaging wavelength. Considered as an "isolated feature". However, there is no generally accepted accurate definition of “dense features”, nor is there a generally accepted accurate definition of “sparse features”.

[0009] Further, the concept of pitch in the present description and claims also applies to clusters of at least two features, where "pitch" is two of two substantially similar adjacent features. Refers to the mutual distance between corresponding points.

[0010] The resolution limit of the projection apparatus is one of the characteristics that determines the CD obtained in a lithographic manufacturing process. A limitation of this resolution, generally indicated wavelength of the radiation of the NA and the projection beam of the projection system, as well as by a process constant k ₁ that varies with the specific process used. A conventional method for improving the resolution is to increase the NA and shorten the wavelength. These means have the side effect that the insensitivity to the residual error of the depth of focus and the exposure dose of the radiation target portion is reduced. The combination of the usable depth of focus and the allowable variation in exposure dose with a given tolerance of the target design feature CD size is usually referred to as process latitude. Preferably, the super-resolution means should not affect process latitude, so the minimum required available process latitude is now another feature that determines the minimum CD that can be obtained in a lithographic manufacturing process. is there.

[0011] One solution to this problem is the use of double patterning technology (DPT). In this way, the dense pattern is divided into one or more partial patterns of less dense features.

[0012] One aspect of an embodiment of the present invention is a method of dividing a lithographic pattern into a plurality of sub-patterns, the method comprising at least one test structure corresponding to one or more structures of interest in the lithographic pattern. Generating, changing at least one test structure via a selected dimension range to generate a plurality of changed test structures, determining a plurality of values for an image quality metric of the images of the plurality of changed test structures; Dividing a lithographic pattern into multiple sub-patterns, including analyzing those values to determine a dimensional range where pattern division improves image quality metric, and generating multiple sub-patterns of the lithographic pattern according to the determined range Provide a method.

[0013] Given the desired pattern, two times based on the division of the desired pattern into two sub-patterns with features less dense than the features of the desired pattern, performed on a given lithographic apparatus The applicability of the exposure step can be evaluated on a measure of process latitude that is minimally required for printing each sub-pattern. In general, the process latitude that allows the printing of a pattern depends on the desired pattern characteristics (such as the range of pitches where CD and CD size features appear in the desired pattern), the characteristics of the lithographic apparatus used (illumination mode, Depending on parameters including the wavelength of the patterned beam, the maximum numerical aperture of the projection system, etc.) and the characteristics of the pattern provided to the reticle (eg, binary pattern or attenuated phase shift pattern). Thus, when process latitude is used as a criterion to enable printing and various lithographic steps are compared, these characteristics must be accounted for.

[0014] Aspects of embodiments of the invention can include a computer-readable medium encoded with computer-executable instructions for performing the method described above or controlling a lithography system according to the method described above.

[0015] Aspects of embodiments of the invention can include a lithography or lithocell system configured and arranged to operate according to the methods described above. Such a system can, for example, incorporate a computer programmed to allow a user to control the device according to this or another method.

[0016] Aspects of embodiments of the present invention may include a simulation system configured and arranged to operate according to the method described above.

[0017] An aspect of an embodiment of the present invention is a method of manufacturing a mask according to the above method, designing a pattern of the mask according to the above dividing method, and describing the pattern of at least one mask according to the determined dividing rule. Can be included.

[0018] Aspects of embodiments of the present invention can include a method of manufacturing a microelectronic device using a pattern derived according to the splitting method described above.

[0019] Aspects of embodiments of the invention can include devices manufactured according to the methods described above.

[0020] Aspects of embodiments of the invention can include a method that includes imaging a segmented pattern according to the method described above.

[0021] A device pattern including multiple features can be decomposed into two sub-patterns using a design rule check or a graph theory algorithm. Such algorithms are available in electronic design automation software used for design evaluation and modification, eg, Optical Proximity Correction. Such a decomposition algorithm is such that the mutual distance between any two adjacent features in the device pattern is at least the critical dimension CD, and any two adjacent features of the first and second sub-patterns obtained after decomposition. It can be used in the present invention when the mutual distance between is at least twice the critical dimension CD. Increasing the mutual distance allows subpattern feature expansion as well as resizing for biasing and / or OPC without exceeding the minimum absorber width limit between two transparent subpattern features. This minimum width is determined by the mask fabrication technique. Currently, a width on the order of 80-100 nm is possible (at the mask level). Alternatively, assist features (i.e. features that do not print scatter bars, etc.) can be placed taking advantage of the increase in mutual distance to further promote optical proximity correction. On the other hand, if there is not enough space between adjacent features, the above arrangement may not have been possible in a desired pattern.

[0022] In the case of a device pattern including a plurality of features, the mutual distance between any two adjacent features of the first and second sub-patterns obtained after decomposition is at least twice the critical dimension CD Although it is not possible to apply decomposition into two subpatterns that satisfy both conditions, it is possible to obtain at least one subpattern that satisfies the conditions. In that case, one sub-pattern that does not satisfy the condition can be further divided, and if necessary, the division can be repeated until each obtained sub-pattern satisfies the condition. In that case, an embodiment of the present invention is not limited to the two-time exposure process, but includes a multi-exposure process that matches the number of sub-patterns that can obtain the number of exposures.

[0023] Although specific reference is made herein to the use of a lithographic apparatus in IC manufacturing, the lithographic apparatus described herein includes an integrated optical system, magnetic domain memory guidance and detection patterns, a liquid crystal display (LCD). It should be understood that other applications may be included, including the manufacture of thin film magnetic heads and the like. As will be apparent to those skilled in the art, in such other applications, the terms “wafer” or “die” as used herein are each a more general “substrate” or “target portion”, respectively. It may be considered synonymous with the term “.” The substrate described herein may be processed before or after exposure, for example, in a track (usually a tool that applies a resist layer to the substrate and grows the exposed resist), or a metrology tool, or inspection tool. May be. The disclosure in the present specification can be appropriately applied to the above substrate processing tool and other substrate processing tools. Further, since the substrate can be processed multiple times, for example, to make a multi-layer IC, the term substrate as used herein can also refer to a substrate that already contains multiple processing layers.

[0024] As used herein, the terms "radiation" and "beam" refer to ultraviolet (UV) radiation (eg, having a wavelength of 365, 248, 193, 157, or 126 nm), and extreme ultraviolet (EUV) Includes all types of electromagnetic radiation, including radiation (eg, having a wavelength in the range of 5-20 nm).

[0025] The term "patterning device" as used herein broadly refers to a device that can be used to apply a pattern to a cross section of a projection beam, for example, to form a pattern on a target portion of a substrate. Should be interpreted. Note that the pattern imparted to the projection beam may not exactly correspond to the desired pattern of the target portion of the substrate. In general, the pattern imparted to the projection beam will correspond to a particular functional layer in a device such as an integrated circuit being created in the target portion.

[0026] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in the lithography art and include mask types such as binary, alternating phase shift, and halftone phase shift, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of small mirrors that can be individually tilted to reflect the incoming radiation beam in various directions. Thus, the reflected beam is patterned.

[0027] The support structure supports the patterning device, ie carries the weight of the patterning device. The support structure holds the patterning device in a manner that is in accordance with the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support can use mechanical clamping, vacuum, or other clamping techniques such as, for example, electrostatic clamping in a vacuum environment. The support structure may be a machine that holds the patterning device, vacuum, electrostatic or other clamping technique. The support structure may be fixed or movable as appropriate, for example, and may be a frame or table that ensures that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

[0028] While the embodiments of the invention will be described with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, this is by way of illustration only.

[0029] FIG. 1 depicts a lithographic projection apparatus according to an embodiment of the invention. [0030] FIG. 5 illustrates a device pattern including an array of square contact holes and two sub-patterns. [0031] FIG. 7 shows ILS simulation results comparing one exposure for all feature pitches and division of all pitches (DPT). [0032] FIG. 6 is a diagram showing exposure latitude (focus vs. dose) in the case of non-division (90 nm pitch, 35 nm CD target) and division pattern (180 nm pitch, 35 nm CD target). [0032] FIG. 7 shows exposure latitude (focus vs. CD) for non-divided (90 nm pitch, 35 nm CD target) and split pattern (180 nm pitch, 35 nm CD target). [0032] FIG. 7 is a diagram showing exposure latitude (focus vs. dose) in the case of non-division (90 nm pitch, 35 nm CD target) and division pattern (180 nm pitch, 35 nm CD target). [0032] FIG. 7 shows exposure latitude (focus vs. CD) for non-divided (90 nm pitch, 35 nm CD target) and split pattern (180 nm pitch, 35 nm CD target). [0033] FIG. 6 shows exposure latitude (depth of focus versus% tolerance) for split (90 nm pitch, 35 nm CD target) and non-split imaging. [0034] FIG. 10 is a diagram showing exposure latitude (focus vs. dose) for non-divided (130 nm pitch, 35 nm CD target) and divided patterns (260 nm pitch, 35 nm CD target). [0034] FIG. 13 shows exposure latitude (focus vs. CD) for non-divided (130 nm pitch, 35 nm CD target) and split patterns (260 nm pitch, 35 nm CD target). [0034] FIG. 10 is a diagram showing exposure latitude (focus vs. dose) for non-divided (130 nm pitch, 35 nm CD target) and divided patterns (260 nm pitch, 35 nm CD target). [0034] FIG. 13 shows exposure latitude (focus vs. CD) for non-divided (130 nm pitch, 35 nm CD target) and split patterns (260 nm pitch, 35 nm CD target). [0035] FIG. 7 shows exposure latitude (depth of focus vs. tolerance%) for undivided (130 nm pitch, 35 nm CD target) and split (260 nm pitch, 35 nm CD target) imaging. [0036] (a)-(e) are diagrams showing examples of test structures and metrics related to the structures. [0037] (a) and (b) are diagrams illustrating examples of test patterns used in accordance with certain embodiments of the present invention. [0038] FIG. 6 illustrates several metrology sites for use in accordance with certain embodiments of the present invention. [0039] FIG. 7 shows ILS simulation data for M4 metrology sites at various pitches. [0040] FIG. 6 is a flow chart illustrating a method according to an embodiment of the invention. [0041] FIG. 6 is an example of a logic standard cell analyzed according to a method according to an embodiment of the invention. [0042] FIG. 6 shows a comparison of potential split imaging processes for simulated dense features of an 85 nm pitch pattern. [0042] FIG. 8 shows process window information for a simulated dense feature imaging process with a pitch pattern of 85 nm. [0042] FIG. 6 shows a comparison of potential split imaging processes for simulated dense features of an 85 nm pitch pattern. [0042] FIG. 8 shows process window information for a simulated dense feature imaging process with a pitch pattern of 85 nm. [0042] FIG. 6 shows a comparison of potential split imaging processes for simulated dense features of an 85 nm pitch pattern. [0042] FIG. 8 shows process window information for a simulated dense feature imaging process with a pitch pattern of 85 nm. [0043] (a)-(c) show simulated patterns with respect to FIGS. 14a-14f.

FIG. 1 is a schematic view of a lithographic projection apparatus that can be used in the method of the present invention. This device
[0045] A radiation system Ex, IL that provides a projection beam PB of radiation (eg, UV radiation or DUV radiation such as radiation having a wavelength of less than about 270 nm, eg, wavelengths 248, 193, 157, and 126 nm), In this particular case, the radiation system also includes a radiation source LA,
A first object table (mask table) MT including a mask holder that holds a mask MA (eg, a reticle);
[0047] a second object table (substrate table) WT including a substrate holder for holding a substrate W (for example, a resist-coated silicon wafer);
[0048] A projection system ("lens") PL (eg, conventional imaging or immersion fluid) that images the irradiated portion of the mask MA onto a target portion C (eg, including one or more dies) of the substrate W. Quartz and / or a CaF ₂ lens system or catadioptric system including lens elements made from materials such as quartz, CaF ₂ suitable for any imaging using
Is provided.

[0049] As shown herein, the apparatus is transmissive (ie, has a transmissive mask). In general, however, the device may be reflective, for example (with a reflective mask). Alternatively, the apparatus may use another type of patterning device such as the programmable mirror array described above.

[0050] The radiation source LA (eg, a UV mercury arc lamp or DUV excimer laser) generates a radiation beam. This beam is incident on the illumination system (illuminator) IL, either directly or after passing through an adjusting optical device such as, for example, a beam expander Ex. The illuminator IL includes an adjustable element AM that sets the outer and / or inner radius range (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the beam. In addition, the illuminator IL typically includes various other components such as an integrator IN and a capacitor CO. Thus, the beam PB hitting the mask MA has a desired uniformity and intensity distribution in its cross section.

[0051] It should be noted with respect to FIG. 1 that the source LA may be within the housing of the lithographic projection apparatus (eg, as is often the case when the source LA is a mercury lamp). However, the source LA may be remote from the lithographic projection apparatus so that the radiation beam it produces is directed into the apparatus (eg with the aid of a suitable guiding mirror). The latter scenario is often used when the source LA is an excimer laser. The present invention and claims include both of these scenarios.

[0052] Thereafter, the beam PB intersects with the mask MA held on the mask table MT. The beam PB beyond the mask MA passes through the lens PL, and the lens PL focuses the beam PB on the target portion C of the substrate W. With the help of a positioner (and interferometer or linear encoder) not explicitly shown in FIG. 1, the substrate table WT can be moved precisely in order to place the various target portions C in the path of the beam PB. . Similarly, using an additional positioner (not explicitly shown in FIG. 1), for example, after mechanical retrieval of the mask MA from the mask library, or during a scan, the mask MA is moved relative to the path of the beam PB. Can be placed accurately. In general, the movement of the object tables MT, WT can be realized with the help of a long stroke module (coarse positioning) and a short stroke module (fine positioning) not explicitly shown in FIG. However, in the case of a wafer stepper (as opposed to a step-and-scan apparatus), the mask table MT need only be connected to a short stroke actuator or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0053] The depicted apparatus can be used in two different modes:
[0054] In the step mode, the mask table MT is basically stationary, and the entire mask image is projected onto the target portion C once (ie, with one “flash”). The substrate table WT is then moved in the x and / or y direction so that another target portion C can be irradiated by the beam PB.
[0055] 2. In scan mode, it is basically the same scenario, but a given target portion C is not exposed in a single “flash”. Instead, the mask table MT can move at a velocity v in a given direction (so-called “scan direction”, eg the y direction). Thereby, the projection beam PB scans the mask image. At the same time, the substrate table WT moves in the same or opposite direction at a speed V = Mv (usually M = 1/4 or 1/5). M is the magnification of the lens PL. Thus, a relatively large target portion C can be exposed without sacrificing resolution.

[0056] As described above, one technique for reducing the effective density of the pattern to be imaged is to use a design rule inspection algorithm to divide the pattern into two subpatterns, each having a relatively low density, and In this method, the pitch of the pattern is made larger than the capability of the lithography system to be used. In general, such partitioning is performed for each feature based on a rule or set of rules that determines which subpattern the feature belongs to. This is called “coloring” the pattern. This is because, in some embodiments, features are colored red or blue depending on which subpattern is assigned. One example is a space-based rule. If two features are within a certain distance of each other, one feature is painted red, the other is painted blue, all red features are assigned to the first subpattern, and all blue features are second Assign to the subpattern.

[0057] In accordance with the prior art rule-based pattern segmentation shown in FIG. 2, a device layer with a desired pattern including a plurality of contact holes comprises a 0.9NA lithographic projection apparatus and a 6% halftone patterning the projection beam. It is printed with an attenuated phase shift mask and with a positive tone resist suitable for use with a projection beam radiation wavelength of 193 nm. In this manner, the device pattern includes a linear array of square contact holes 20 with sides 27 as shown in FIG. The minimum dimension of each contact hole is the length of the side 27. In this example, this length is 90 nm corresponding to the critical dimension CD. In the pattern 10, as indicated by the arrow 21, the contact holes are separated by at least a distance CD. In FIG. 2, the minimum pitch existing in the pattern 10 is denoted as P and indicated by an arrow 24. Here, P = 2CD. The pattern further includes contact holes 20 spaced apart from any contact holes present in the pattern 10 and spaced apart from each other at a pitch larger than P.

The pattern 10 is divided into first and second sub-patterns 31 and 32 using a commercially available design inspection rule tool. The mutual distance between adjacent contact holes of patterns 31 and 32 is indicated by arrows 22 and 23. This distance is 3CD. Patterns 31 and 32 have pitches P1 and P2 indicated by arrows 25 and 26, respectively. Here, P1 = P2 = 2P = 4CD. Accordingly, the pitch of the sub-pattern is expanded twice.

[0059] As a result of the above rule-based approach, one or both of the sub-patterns incorporating a so-called forbidden pitch is obtained. For a given lighting setting, the forbidden pitch exists where the field created by the adjacent feature destructively interferes with the main feature field. As a result, when pattern division is applied, a decrease in ILS (image log slope) may occur.

[0060] FIG. 3 is a diagram of ILS vs. pitch simulation data illustrating the above problem. The simulated illumination is a NA 1.35 cross quadrupole (C-quad) with σ _out = 0.98 and σ _in = 0.83. According to the rules applied, feature pairs with a pitch of 100 nm or less are split, and features with a pitch greater than 100 nm are not split.

[0061] Referring to the figure, the ILS is plotted against the pitch and, as a result of the scan, the ILS for a split pattern of ILS (2P or 160-180 nm imaging) at a certain pitch (eg, 80-90 nm). It can be seen that the image quality decreases (that is, the image quality decreases). Furthermore, as a result of scanning, ILS should have improved if division was applied at certain pitches (eg, 130-140 nm) that were not divided by the applied rule. As a result, for certain patterns and image devices, this rule cannot achieve the best possible image quality.

[0062] Figures 4a and 4b show similar results for exposure latitude. At a 90 nm pitch, a feature with a 35 nm CD must split the 90 nm feature, applying the same 100 nm split rule. Comparing FIG. 4a (undivided) with FIG. 4b (divided), it can be seen that this division should not be performed and that the exposure latitude is reduced by the division.

[0063] FIG. 5 shows a process window for a 90 nm pitch, 35 nm CD. Compared to division at this pitch, the exposure latitude does not increase much, but the 100 nm rule states that this pattern should be divided. This is consistent with the conclusions obtained from FIGS. 4a and 4b and FIG.

[0064] Inverse examples are shown in Fig. 6a (undivided), Fig. 6b (divided) and Fig. 7. In these figures, it is shown that the exposure latitude is larger in the divided pattern than in the non-divided pattern in the case of the 130 nm pitch pattern having the target CD of 35 nm. Dividing a pattern having a pitch that is not in the division rule improves the image quality, and is also consistent with FIG.

[0065] According to an embodiment of the invention, several test structures are generated. There are various test structures, and simulated aerial image data is generated from the various test structures. From the simulated image data, segmentation rules are formulated and applied to the design to select features for each subpattern.

[0066] FIGS. 8a-8e illustrate several test structures that can be used in certain embodiments of the present invention and dimensions that vary in these structures. Examples of variable dimensions include pitch (FIG. 8a), line-to-line (FIG. 8b), end-to-end (FIG. 8e), end-to-line (FIG. 8d), and corner-to-corner (FIG. 8e) dimensions.

[0067] FIG. 9a shows an example of a generated set of features that have been modeled and FIG. 9b is an enlarged view of the right feature set of FIG. 9a. In FIG. 9a, the pitch increases on the axis from the top to the bottom of the figure. The pitch of the top feature set is 62 nm, while the pitch of the bottom feature set is 66 nm.

[0068] After executing the simulation, a report is generated based on the structure, as shown in FIG. As can be seen from FIG. 10, there are several metrology sites M1-M6 for determining the quality of the simulated image. In the illustrated example, M1 is the area between the ends, M2 is the space, M3 is the area between the ends, M4 is related to the pitch, and M5 and M6 are the areas between the corners. For example, the report may include information about the location of each metrology site (eg, XY coordinates), single exposure, double exposure, both, and ILS before and after applying the optimal proximity correction. Finally, if the ILS is high in a single exposure, an ILS measurement may be further performed before and after the OPC without using the double exposure technique.

An example of the ILS simulation of the M4 test structure is shown in FIG. As can be seen from this figure, below about 80 nm, DPT improves ILS. On the other hand, between about 80 nm and about 100 nm (that is, between pitch 1 and pitch 2), the ILS indicated by the DPT is lower than the single exposure. Furthermore, between about 100 nm and 150 nm, DLS improves ILS. This indicates that this region should be divided, contrary to the premise of the 100 nm rule that was originally proposed. The region indicated by 100 is the region with the lowest ILS, which is considered to be a “need to be divided” range.

When these correction rules are determined, the process proceeds by applying the optical proximity effect correction technique to the pattern and verifying that the derived division rule is correct. The same workflow can be applied to each of the other metrology sites, and split rules can be derived for the remaining split criteria. If desired, the user can assign metrology priorities such that, for example, performance between edges is more important than that between corners. It will be appreciated that the preferred metrology sites will vary depending on the actual structures that are imaged according to the process design and the importance of those structures to the function of the final device to be manufactured.

[0071] FIG. 12 is a flow diagram illustrating an exemplary workflow of a method according to an embodiment of the invention. The process starting from the target design 115 proceeds to the creation of the test design 120 based on, for example, the division determination criterion parameter specified by the user. For example, the parameter may include a plurality of metrology positions M ₁ . . . It may be based on M _n . With the selected metrology location, the method proceeds to ILS or NILS (eg) 125. Next, the method proceeds to analysis 130 of evaluation results by pitch and space. Based on the analysis, the method proceeds to identify 135 the minimum and maximum ILS (or NILS) for each metrology site.

[0072] Once the sites are identified, the entire pattern can be divided into sites that match the criteria that are excluded from the application of the splitting rules and sites that do not match the criteria that ensure that they are split according to the splitting rules. In some embodiments, this may include placing 140 a coloring block layer at a site having better ILS and placing 145 a marker layer at a site having relatively poor ILS. Once the site is so divided, the application of coloring rules taking into account ILS can be performed 150. Next, the ILS can be evaluated 155 for the split pattern, and the ILS can be performed 160 for all metrology sites before and after the split. If the ILS of certain sites is not improved or deteriorates, the procedure returns to the step of deriving the coloring rules and those sites are excluded from the split operation. As each site is optimized according to this iterative process, stitching and optical proximity correction elements are applied 165 as appropriate. After the OPC features are included, the ILS can be re-verified 170 on the split pattern.

[0073] FIG. 13 is an example of an ILS diagram of a standard logic cell divided by an ILS base rule according to an embodiment of the present invention. In this figure, the broken line 175 represents the coloring block layer of the pattern division, and the solid line 180 represents the other color of the two pattern division.

[0074] FIGS. 14a-14f are diagrams of an example where splitting reduces the process window, similar to the situation shown in FIGS. 4a, 4b, and 5. FIG. In this example, FIG. 14a shows a Bossung curve for imaging a series of dense features with a pitch of 85 nm (ie, the pattern shown in FIG. 15a). In the example of FIG. 14a, the illumination is optimized for dense pitch imaging. From the calculated curve, it can be seen that a depth of focus of 340 nm can be achieved with an exposure latitude of 8%. From the same data, the exposure latitude window shown in FIG. 14b can be improved. As can be seen in the figure, the exposure latitude window in the illustrated example is relatively symmetric and the elliptical process window is relatively large.

[0075] In contrast, the Bossung curve of the split pattern including assist features (170 nm pitch including assist features shown in FIG. 15b) actually causes process window degradation. From FIG. 14c, the depth of focus at 8% exposure latitude is significantly reduced to about 90 nm. Similarly, the process window shown in FIG. 14d is slightly less symmetrical than the process window of FIG. 14b, and the elliptical process window has a much shorter depth of focus even though the dose is similar.

[0076] FIGS. 14e and 14f are similar to FIGS. 14c and 14d, but show a process window for a split pattern without the assist features shown in FIG. 15c. As can be seen from the figure, this process window is much less symmetrical than the process window of the split pattern with assist features. Furthermore, the depth of focus achievable with 8% exposure latitude is reduced to 60 nm, while the dose tolerance is not significantly different from the remaining two examples. More interestingly, the doses required in the examples of FIGS. 14e-14f are somewhat larger (unlike the other two examples, which are concentrated around 53.25 and 53.88, respectively). doing). For all three steps, the process window is maximized at about -0.1 defocus.

[0077] Considering the calculated process window, for a particular dense feature imaging of the example of FIGS. 14a-14f, where a dense pitch is printed in a single exposure using an optimal radiation source, this book It is clear that the ILS-based splitting rules described herein should determine that there are no pattern splits that degrade rather than improve the process window.

[0078] According to certain embodiments of the invention, the method may be performed by a software module configured to perform the partitioning algorithm described herein. A software module may be implemented in the form of machine-executable instructions stored on a machine-readable medium. The module can be configured to execute a partitioning algorithm, and additional modules implemented in a common computer system or implemented in the lithographic apparatus itself are described herein by operating the lithographic apparatus. The device can be configured to image the device on the substrate using a mask designed according to the method.

[0079] According to an aspect of the present invention, the increase in the minimum available space between features in the matching subpattern relative to the minimum available space between features in the desired pattern is an assist feature into the matching subpattern. (I.e. features that do not print scatter bars etc.) may be used to provide optical proximity correction, while the lack of space between features results in the desired pattern It may have been impossible to make such an arrangement within.

[0080] In a chip manufacturing process according to an embodiment of the present invention, the exposed radiation-sensitive layer is subjected to a resist process to provide a corresponding array of resist-processed features. The result is an array of features with the desired pitch. In certain applications, the feature may be a contact hole, for example.

[0081] While specific embodiments of the invention have been described, it will be appreciated that the invention may be practiced otherwise than as described. The description is not intended to limit the invention. For example, although the above example focuses on ILS and NILS as image quality measurement, an appropriate division rule to be applied can be determined using MEF and other image quality metrics in the same manner. Furthermore, this method is generally applicable beyond the example of line / space type patterns, such as contact / via patterns.

Claims (16)

A method of dividing a lithographic pattern into a plurality of sub-patterns,
Generating at least one test structure corresponding to one or more structures of interest in the lithographic pattern;
Wherein varying the at least one test structure by varying within a certain range the dimensions relating to the structure, generating a plurality of variation test structure,
Determining a plurality of values for an image quality metric of the plurality of change test structure images;
Analyzing the plurality of values to determine a dimensional range in which pattern division improves the value of the image quality metric;
It involves dividing the lithographic pattern to the plurality of sub-patterns of the lithographic pattern according to the determined size range, method.   The method of claim 1, wherein the image comprises a simulated image. Determining a value of a sub-pattern image quality metric for each image of the sub-pattern;
Comparing the value of the sub-pattern image quality metric of the sub-pattern with the value of the image quality metric of the image;
Based on the comparison, determining whether the value of the image quality metric is improved as a result of the sub-pattern;
The method of claim 1, further comprising: Dimensions relating to the structure, pitch, between the lines, between the ends, including the dimensions selected from the group consisting of between and between the corner of the end portion and the line, according to any one of claims 1 3 Method.   The method according to claim 1, wherein the determination of the value of the image quality metric determines the value of the image quality metric at a plurality of locations in the image. Wherein the plurality of locations, have different types of dimensions for the structure, the method further comprises assigning a priority between the different types of sizes, the method according to claim 5.   The method of any one of claims 1 to 6, wherein the generated sub-pattern further includes additional assist features that are not within the lithographic pattern.   The method of claim 7, wherein the assist feature comprises a sub-pattern resolution feature.   9. The method according to any one of claims 1 to 8, wherein the image quality metric comprises an image quality metric selected from the group consisting of ILS, NILS and MEF. First further comprise producing a mask corresponding to the subpattern, the method according to any one of claims 1 to 9 of the plurality of sub-patterns. The method of any one of claims 1 to 9 , further comprising manufacturing a set of masks, each mask corresponding to a sub-pattern of the plurality of sub-patterns. 12. A method comprising imaging a sub-pattern of a mask produced by the method of claim 10 or 11 onto a photosensitive layer on a substrate using a photolithography apparatus. Imaging at least one additional mask sub-pattern, each additional mask corresponding to a remaining sub-pattern of the plurality of sub-patterns;
Processing the substrate to improve the imaged sub-pattern so that the lithographic pattern is reproduced in the photosensitive layer on the substrate;
The method according to claim 10 or 11 , further comprising: The method of claim 13 , further comprising manufacturing a microelectronic device using the processed substrate and the reproduced lithographic pattern.   A mask manufactured by the method according to claim 10.   A set of masks produced by the method of claim 11.

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